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Simple science boosts vegetable crops

With a little time, a bit of dye and a good eye, vegetable farmers can learn to grow their crops more efficiently and economically, says a University of Georgia scientist.

Vegetable farmers in south Georgia and Florida can grow crops in all seasons because of the subtropical climate, said Alex Csinos, a plant pathologist with the UGA College of Agricultural and Environmental Sciences.

Of the 200,000 acres of vegetables grown in Georgia, about 20 percent are grown in raised beds of soil wrapped in plastic, called polyethylene film mulch. And the percentage is growing.

The practice allows the farmer to better control the environment for the crop and apply things like fertilizers, pesticides, fungicides and water in a more environmentally friendly way.

To do this, farmers run a thin hose with small emitters through the bed under the plastic. They then inject this “drip tape” with the materials, which drip out into the bed.

But a major blank in this new method needed to be filled.

Because the drip tape was under the plastic and often under soil and emitting colorless materials, nobody could say for sure whether the drip tape got enough of the material to the plant or into the raised bed.

How much material should run through the tape? For how long? At what pressure? Is the tape emitting enough materials to effectively cover the bed? The answers could mean the difference between a good crop and no crop at all.

The instructions salesmen gave to farmers were “best guesses,” Csinos said. “At the time, there was no scientific data to back up what they were saying, or selling.”

So Csinos took some simple blue dye and injected it through some drip tape under plastic on a raised bed at the UGA Tifton, Ga., campus. He then sliced down through the bed in various places. The blue designs in the sliced pieces of the bed showed exactly where the material was being deposited.

“Now we can say with much more certainty how effective the drip tape is in delivering materials to the bed under the plastic,” Csinos said.

Sandy soils pose a problem to Georgia and Florida, said Johan Desaeger, a post-doctoral scientist working with Csinos. Fluids tend to drop straight through them. Georgia's soil can be as much as 88 percent sand. Florida's can be 98 percent sand.

Most raised vegetable beds are about 32 inches wide. To control vegetables' top two enemies, nutsedge and nematodes, the entire bed needs to be fumigated. Nematodes are microscopic worms that feed on plant roots. Nutsedge is a weed.

Initial studies in sandy soils showed that in many cases the drip tape wasn't delivering enough material to spread adequately over the entire bed.

“And when you don't treat the entire bed, those pathogens outside the range of the drip tape survive and just come straight back to that area once the material has leached through,” Csinos said.

Science doesn't have to be complicated. It just has to be effective. Csinos, Desaeger and other UGA researchers have put many different drip tapes through the blue-dye test. And many more scientists and farmers have used this method in Georgia, Florida and South Carolina.

Pesticide manufacturers now use results from this simple scientific method to write better directions for drip tape usage on their labels.